Wireless USB hardware scheduling

Abstract

In wireless USB data transfers over UWB, software configures hardware thresholds to control data transfer in a manner that uses bandwidth for good connections over bad connections, given the high error rate experienced with wireless USB. Periodic transfers are first attempted before asynchronous transfers, as long as the periodic transfers are successful. When failures are occurring, the hardware includes a mechanism having a software-configurable threshold specifying the number of errors a given endpoint can tolerate before it is paused in the schedule. By pausing transfer attempts that are likely to again fail, endpoints with successful transfers are favored over those experiencing errors. When the number of active transfers pending exceeds a software-configurable notification threshold for isochronous endpoints, the hardware notifies the software of this state, corresponding to a low-buffer condition at the receiver. The software may then reconfigure thresholds and deactivate other transfers to force data transfers into the buffer.

Description

FIELD OF THE INVENTION [0001] The invention relates generally to communicating data between computer systems and peripheral devices via wireless communications. BACKGROUND [0002] Almost all contemporary computer systems are configured to use USB (Universal Serial Bus), an external peripheral interface standard for serial communication between computer systems and external peripheral devices such as a mouse, a printer, a digital camera, and so forth. With USB, each peripheral device connects via a cable that plugs into a standardized USB port on the computer system. [0003] In an effort to eliminate the need for USB cables to connect computers systems and the external peripherals, wireless USB (or WUSB) based on ultrawideband (UWB) technology is becoming standardized. Wireless USB is directed towards having communication speeds comparable to the USB 2.0 standard, e.g., 480 Mbps, over distances up to ten meters. [0004] However, unlike wired USB where transmission errors are extremely r...

AI Technical Summary

Benefits of technology

[0006] Briefly, the present invention is directed towards a system and method by which hardware and software on a computer system work together to schedule USB wireless data transfers, in which failed transfers are retried in a controlled manner. Because wireless USB transfers are buffered at the receiving end, a successful retry supplies missing data for insertion into an appropriate position in the buffer. By retrying failed transfers in a controlled manner, in ordinary operation bandwidth is not wasted on retry attempts on connections that will most likely fail, but instead is used for connections that will likely succeed. However, in critical situations such as a low buffer condition at the receiving device, the controlling software can change the configurable scheduling parameters to force data transfer over the corresponding connection.

[0008] To schedule the various data transfers, the present invention comprises a wireless USB component in the hardware, and a wireless USB controller driver in the software. The wireless USB hardware includes a scheduling process that manipulates information in queue head data structures that correspond to endpoints, based on whether their associated packets were successfully received. The hardware scheduling process includes a mechanism having a software-configurable threshold that specifies the number of errors a given queue head (corresponding to an endpoint) can tolerate during a time period before the queue head is paused in the schedule such that packets associated with other queue heads may be transferred. The scheduling process thus handles retries of failed transfers in a software-controlled manner that avoids wasting bandwidth on data transfers that are likely to fail due to transient error conditions. The software controller driver also configures other information (e.g., thresholds) in the data structures.

[0011] Software controls the hardware operation by writing to various threshold parameters, including an error count threshold that determines when to pause a queue head. More particularly, when an error counter in a queue head that was initialized with this threshold and is decremented on an error transitions from one to zero, that particular queue head is paused (no longer retried), which may be for the remainder of the time slot. Pausing allows other queue heads' packets to be transferred in the time slot, rather than reattempting transfer over a connection that has met the threshold error level and is thus likely to again fail. A paused queue head moves out of its paused state either at the beginning of the next time slot, or after the other endpoints (queue heads' packets) in the current time slot have been exhausted via success, pausing or halting and there is still remaining time (corresponding to available bandwidth) in the time slot that would be otherwise unused. Pausing a queue head in response to failed transfers thus allows the schedule to prefer endpoints that are able to successfully transfer packets over endpoints that are not.

[0017] As can be seen, periodic transfers are attempted first, but queue heads that fail a threshold number of times are paused (or halted), so as to not waste available bandwidth by making repeated transfer attempts that are likely to again fail. The remaining time is instead used for attempting asynchronous transfers, which are similarly paused (or halted) if failing. The present invention thus may alternate between periodic transfer attempts and asynchronous failure attempts as necessary within a time slot, but in a controlled manner.

Problems solved by technology

To provide an acceptable computing experience with wireless USB, the high error rate in data transfer requires that retries be performed, even on isochronous transfers, in which delivery is not guaranteed.

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